Fibroblast growth factors (FGFs) and their receptors (FGFRs) play critical roles during embryonic development, tissue homeostasis and metabolism (1-3). In humans, there are 22 FGFs (FGF1-14, FGF16-23) and four FGF receptors with tyrosine kinase domain (FGFR1-4). FGFRs consist of an extracellular ligand binding region, with two or three immunoglobulin-like domains (IgD1-3), a single-pass transmembrane region, and a cytoplasmic, split tyrosine kinase domain. FGFR1, 2 and 3 each have two major alternatively spliced isoforms, designated IIIb and IIIc. These isoforms differ by about 50 amino acids in the second half of IgD3, and have distinct tissue distribution and ligand specificity. In general, the IIIb isoform is found in epithelial cells, whereas IIIc is expressed in mesenchymal cells. Upon binding FGF in concert with heparan sulfate proteoglycans, FGFRs dimerize and become phosphorylated at specific tyrosine residues. This facilitates the recruitment of critical adaptor proteins, such as FGFR substrate 2 α (FRS2α), leading to activation of multiple signaling cascades, including the mitogen-activated protein kinase (MAPK) and PI3K-AKT pathways (1, 3, 4). Consequently, FGFs and their cognate receptors regulate a broad array of cellular processes, including proliferation, differentiation, migration and survival, in a context-dependent manner.
Aberrantly activated FGFRs have been implicated in specific human malignancies (1, 5). In particular, the t(4;14) (p16.3;q32) chromosomal translocation occurs in about 15-20% of multiple myeloma patients, leading to overexpression of FGFR3 and correlates with shorter overall survival (6-9). FGFR3 is implicated also in conferring chemoresistance to myeloma cell lines in culture (10), consistent with the poor clinical response of t(4;14)+ patients to conventional chemotherapy (8). Overexpression of mutationally activated FGFR3 is sufficient to induce oncogenic transformation in hematopoietic cells and fibroblasts (11-14, 15), transgenic mouse models (16), and murine bone marrow transplantation models (16, 17). Accordingly, FGFR3 has been proposed as a potential therapeutic target in multiple myeloma. Indeed, several small-molecule inhibitors targeting FGFRs, although not selective for FGFR3 and having cross-inhibitory activity toward certain other kinases, have demonstrated cytotoxicity against FGFR3-positive myeloma cells in culture and in mouse models (18-22).
FGFR3 overexpression has been documented also in a high fraction of bladder cancers (23, 24). Furthermore, somatic activating mutations in FGFR3 have been identified in 60-70% of papillary and 16-20% of muscle-invasive bladder carcinomas (24, 25). In cell culture experiments, RNA interference (11, 26) or an FGFR3 single-chain Fv antibody fragment inhibited bladder cancer cell proliferation (27). A recent study demonstrated that an FGFR3 antibody-toxin conjugate attenuates xenograft growth of a bladder cancer cell line through FGFR3-mediated toxin delivery into tumors (28). However, it remains unclear whether FGFR3 signaling is indeed an oncogenic driver of in vivo growth of bladder tumors. Moreover, the therapeutic potential for targeting FGFR3 in bladder cancer has not been defined on the basis of in vivo models. Publications relating to FGFR3 and anti-FGFR3 antibodies include U.S. Patent Publication no. 2005/0147612; Rauchenberger et al, J Biol Chem 278 (40):38194-38205 (2003); WO2006/048877; Martinez-Torrecuadrada et al, (2008) Mol Cancer Ther 7(4): 862-873; WO2007/144893; Trudel et al. (2006) 107(10): 4039-4046; Martinez-Torrecuadrada et al (2005) Clin Cancer Res 11 (17): 6280-6290; Gomez-Roman et al (2005) Clin Cancer Res 11:459-465; Direnzo, R et al (2007) Proceedings of AACR Annual Meeting, Abstract No. 2080; WO2010/002862. Crystal structures of FGFR3:anti-FGFR3 antibody are disclosed in co-owned U.S. patent application Ser. No. 13/572,557 (U.S. Patent Publication No. 2012/0321606) filed Aug. 10, 2012 as a continuation of U.S. patent application Ser. No. 12/661,852 (U.S. Patent Publication No. 2010/0291114), filed Mar. 24, 2010.
It is clear that there continues to be a need for agents that have clinical attributes that are optimal for development as therapeutic agents. The invention described herein meets this need and provides other benefits.
All references cited herein, including patent applications and publications, are incorporated by reference in their entirety.